This invention relates in general to the treatment of a production interval of a wellbore to stimulate hydrocarbon production and prevent the production of fine particulate materials and, in particular, to an apparatus and method for sequentially fracturing the production interval then substantially completely gravel packing the wellbore adjacent to the production interval.
It is well known in the subterranean well drilling and completion art that relatively fine particulate materials may be produced during the production of hydrocarbons from a well that traverses an unconsolidated or loosely consolidated formation. Numerous problems may occur as a result of the production of such particulates. For example, the particulates cause abrasive wear to components within the well, such as tubing, pumps and valves. In addition, the particulates may partially or fully clog the well creating the need for an expensive workover. Also, if the particulate matter is produced to the surface, it must be removed from the hydrocarbon fluids using surface processing equipment.
One method for preventing the production of such particulate material to the surface is gravel packing the well adjacent the unconsolidated or loosely consolidated production interval. In a typical gravel pack completion, a sand control screen is lowered into the wellbore on a workstring to a position proximate the desired production interval. A fluid slurry including a liquid carrier and a relatively coarse particulate material, which is typically sized and graded and which is referred to herein as gravel, is then pumped down the workstring and into the well annulus formed between the sand control screen and the perforated well casing or open hole production zone.
The liquid carrier either flows into the formation or returns to the surface by flowing through a wash pipe or both. In either case, the gravel is deposited around the sand control screen to form the gravel pack, which is highly permeable to the flow of hydrocarbon fluids but blocks the flow of the fine particulate materials carried in the hydrocarbon fluids. As such, gravel packs can successfully prevent the problems associated with the production of these particulate materials from the formation.
It is sometimes desirable to perform a formation fracturing and propping operation prior to or simultaneously with the gravel packing operation. Hydraulic fracturing of a hydrocarbon formation is sometimes necessary to increase the permeability of the production interval adjacent the wellbore. According to conventional practice, a fracture fluid such as water, oil, oil/water emulsion, gelled water or gelled oil is pumped down the work string with sufficient pressure to open multiple fractures in the production interval. The fracture fluid may carry a suitable propping agent, such as sand or gravel, which is referred to herein as a proppant, into the fractures for the purpose of holding the fractures open following the fracturing operation.
The fracture fluid must be forced into the formation at a flow rate great enough to fracture the formation allowing the entrained proppant to enter the fractures and prop the formation structures apart, producing channels which will create highly conductive paths reaching out into the production interval, and thereby increasing the reservoir permeability in the fracture region. As such, the success of the fracture operation is dependent upon the ability to inject large volumes of hydraulic fracture fluid into the surrounding formation at a high pressure and at a high flow rate.
For most hydrocarbon formations, a successful fracture and propping operation will require injection flow rates that are much higher than those required for gravel packing. For example, in typical gravel packing, a single pump capable of delivering one to ten barrels per minute may be sufficient. On the other hand, for a successful fracturing operation, three or four large capacity pumps may be required in order to pump at rates higher than the formation fracture gradient which may range up to 60 barrels per minute or more.
It has been found that it is difficult to achieve a complete gravel pack of the desired production interval as part of or following a fracturing operation and particularly in long or inclined/horizontal production intervals. These incomplete packs are commonly a result of the liquid carrier entering the permeable portions of the production interval causing the gravel to form a sand bridge in the annulus. Thereafter, the sand bridge prevents the gravel pack slurry from flowing to the remainder of the annulus which, in turn, prevents the placement of sufficient gravel in the remainder of the annulus.
Therefore a need has arisen for an apparatus and method that are capable of fracturing a production interval. A need has also arisen for such an apparatus and method that produce a complete gravel pack of the wellbore adjacent to the production interval following the fracturing of the production interval. Further, a need has arisen for an apparatus and method that are capable of sequentially stimulating of the production interval then gravel packing the production interval to prevent the production of fine particulate materials when production commences.
The present invention disclosed herein comprises an apparatus and method that are capable of fracturing a production interval and producing a complete gravel pack of the wellbore adjacent to the production interval following the fracturing operation. Specifically, the apparatus and method of the present invention are used to sequentially pack the interval of a wellbore by first delivering a large volume of fracture fluids at a high flow rate and at a pressure above the fracture pressure of the formation then delivering a gravel packing slurry at a lower flow rate. The gravel packing slurry is delivered through a gravel packing apparatus which allows for the complete gravel packing of the interval.
Even though the present invention utilizes a gravel packing assembly to deliver the gravel packing slurry, the high flow rate fracture fluid is not delivered through the gravel packing assembly as prior art attempts to deliver both the fracture fluids at the high flow rates then the gravel packing slurry at the lower flow rate through a gravel packing assembly have not been successful and have resulted in low quality fractures of the formation, incomplete gravel packs or both. Instead, the present invention allows high volume fluid delivery of fracture fluids directly into the wellbore but also allows lower volume delivery of the gravel packing slurry into the wellbore via a gravel packing assembly.
The apparatus for sequentially packing an interval of a wellbore comprises a cross-over assembly partially disposed within a cross-over packer assembly. The cross-over assembly has a set of fracture fluid exit ports and a set of gravel packing exit ports positioned on one side of the packer and a return port positioned on the other side of the packer. The cross-over assembly has a fracturing configuration wherein the fracture fluid exit ports are open, the gravel packing exit ports are closed and the return port either open or closed depending upon the service tool setup. In the fracturing configuration, fracture fluids are delivered through the cross-over assembly via the fracture fluid exit ports directly into the wellbore such that the formation can be fractured. The return ports may be opened to allow for surface pressure monitoring of the annulus between the casing and the work string.
The cross-over assembly also has a gravel packing configuration wherein the fracture fluid exit ports are closed, the gravel packing slurry exit ports are open and the return port is open. In the gravel packing configuration, the gravel slurry is delivered through the gravel packing exit ports into a gravel packing assembly. The gravel packing assembly, which is positioned adjacent to a sand control screen, has a plurality of outlets that are located proximate the sand control screen and that extend along the gravel packing assembly substantially the length of the sand control screen such that the gravel packing slurry is delivered to multiple locations within the wellbore bypassing any sand bridge formation. In the gravel packing configuration, a wash pipe may be disposed within the sand control screen to take returns. The wash pipe is in fluid communication with the return port when the cross-over assembly is in the gravel packing configuration.
Operation of the cross-over assembly from the fracturing configuration to the gravel packing configuration may be achieved in a variety of ways such as through the use of a sliding sleeve, the operation of valves and the like. Likewise, the gravel packing assembly may have a variety of configuration so long as it is capable of overcoming the formation of sand bridges. For example, the distribution of the gravel slurry to multiple location along the length of the sand control screen may be accomplished using a gravel packing assembly having a plurality of conduits having numerous outlets, using a gravel packing assembly having an axially extending slurry passageway and an axially extending production pathway between inner and outer tubulars or using other similar gravel packing assemblies.
In the method of the present invention, sequential fracturing and gravel packing an interval of a wellbore is achieved by traversing a formation with the wellbore, locating a sand control screen within the wellbore proximate the formation, disposing a sequential packing apparatus proximate the sand control screen, positioning the sequential packing in a first position wherein a first exit port is open and a second exit port is closed, pumping a fluid slurry containing propping agents into the sequential packing apparatus such that the fluid slurry containing propping agents exits through the first port at a pressure above the fracture pressure of the formation, operating the sequential packing apparatus from the first position to the second position wherein the first exit port is closed and the second exit port is open, pumping a fluid slurry containing gravel into the sequential packing apparatus such that the fluid slurry containing gravel exits through the second port and discharging the fluid slurry containing gravel into a gravel packing assembly.